The aim of this project was to compare the characteristics of mental health and physical health participants attending an exercise referral scheme (ERS) and investigate associations with their adherence to exercise. While people referred to an ERS with a mental health diagnosis have similar initial rates of uptake as physical health participants, they are more likely to drop out. Comparisons of the groups to understand their differences and how these might impact on their adherence have been limited by the typically low numbers of mental health referrals in many schemes. Retrospective analysis of a participant cohort. Data were extracted on all participants enrolled over a 12- month period (n = 701) and included measurements at baseline, mid-point (13 weeks) and end of programme (20-26 weeks). Differences were explored between the mental health (n=141) and physical health (n=560) subcohorts, and between adherers and non-adherers in each group. Mental health referrals were more likely to be younger, White and unemployed, and had a lower mean body mass index and lower proportion of participants with high blood pressure. They were also more likely to drop out. While occupation was associated with exercise adherence among the physical health group, no predictive factors were identified in the mental health group. While no factors were found to be predictive of their exercise adherence, an understanding of their distinguishing characteristics and attendance behaviour can guide in making better referral decisions concerning them and planning more appropriately tailored support.